NISSAN MAXIMA NOISE PROBLEM

1996 Nissan Maxima • 120,000 miles

My 1996 Nissan Maxima, six cylinder, with 120K miles makes a whistling noise once it warms up, a couple of minutes after the noise starts the radiator cooling fans turn on and about another 30 seconds the noise stops. About one minute later the fans turn off. A couple of minutes later the noise returns and the cycle repeats itself. What could be causing this?